ESTRO 2025 - Abstract Book

S3688

Physics - Quality assurance and auditing

ESTRO 2025

Conclusion: The remote audits showed optimal performance of Italian RT centres, with a few exceptions due to user errors. This experience underlines the need to re-establish the Italian dosimetry audit service provided by ENEA to monitor the quality of the dose delivered by Italian RT centres. Acknowledgments AIFM acknowledges the IAEA Dosimetry Laboratory for the temporary support.

Keywords: multicentric, audit, reference condition

References: IZEWSKA, Joanna; LECHNER, Wolfgang; WESOLOWSKA, Paulina. Global availability of dosimetry audits in radiotherapy: The IAEA dosimetry audit networks database. PHIRO, 2018, 5: 1-4. CLARK, Catharine H.; JORNET, Núria; MUREN, Ludvig P. The role of dosimetry audit in achieving high quality radiotherapy. PHIRO, 2018, 5: 85-87. Dimitriadis A, Kazantsev P, Chelminski K, et al. IAEA/WHO postal dosimetry audit methodology for electron beams using radio photoluminescent dosimeters. Med Phys. 2023; 50: 7214–7221

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Proffered Paper Advancing Accuracy: A comprehensive audit program for carbon ion radiation therapy Paige A Taylor 1 , Shannon Hartzell 2 , Stephen F Kry 1 , Mario Ciocca 3 , Alfredo Mirandola 3 , Giuseppe Magro 3 1 Radiation Physics, UT MD Anderson Cancer Center, Houston, USA. 2 Radiation Oncology, Mayo Clinic Florida, Jacksonville, USA. 3 Radiation Oncology, Centro Nazionale di Adroterapia Oncologica, Pavia, Italy Purpose/Objective: Preliminary data from carbon ion therapy centres show promise of therapeutic advantage for cancer treatment, but there is a gap in external peer review for carbon ion therapy. Existing audit programs have revealed common errors in other radiotherapy modalities: inaccurate dose calculation algorithms, poor beam modelling, and failure to account for anatomical motion properly. Carbon ion therapy is not immune to these errors, and is prone to others, such as range uncertainties and variability in RBE modelling. Material/Methods: A comprehensive carbon ion audit program was developed and tested at the Centro Nazionale di Adroterapia Oncologica in Pavia, Italy. The audit includes a TLD-100 output check, an HU-RLSP calibration validation, an anthropomorphic end-to-end phantom audit (testing heterogeneity with TLD and radiochromic film), an on-site dosimetric audit (testing calibration, lateral profiles, range), and a novel measurement-based microdosimetric validation of RBE model using a tissue-equivalent proportional counter (TEPC, LET-1/2). For the RBE evaluation, we derived linear and quadratic parameters of the cell survival term (α and β) for each considered RBE model (MKM, LEM, and RMF) as well as lineal energy scored in the TEPC based on Monte Carlo simulations of clinically realistic carbon beams. We then fitted these parameters as functions of y* using polynomial equations, establishing a predictive framework for RBE estimation based on microdosimetric measurements. Results: The TLD-based output checks, performed in both monoenergetic or modulated carbon ion beams, achieved an accuracy of 3.9% (1-sigma). The HU-RLSP calibration validation had an accuracy of 4.2% and can catch errors in the low-density (lung) or high-density (bone) regions. The anthropomorphic pancreas phantom (Figure 1) containing a pancreas head target and organs-at-risk measured TLD dose within 1.3% of reference ion chamber measurements.